1. Field of the Invention
The subject invention relates to hydraulic drives, tools and other hydraulic equipment, to methods and apparatus for retrofitting hydraulic drives and tools, to retrofitted hydraulic drives and tools and methods for retrofitting a hydraulic drive with an on-off switching or valving facility.
2. Disclosure Statement
This disclosure statement is made pursuant to the duty of disclosure imposed by law and formulated in 37 CFR 1.56(a). No representation is hereby made that information thus disclosed in fact constitutes prior art inasmuch as 37 CFR 1.56(a) relies on a materiality concept which depends on uncertain and inevitably subjective elements of substantial likelihood and reasonableness, and inasmuch as a growing attitude appears to require citation of material which might lead to a discovery of pertinent material though not necessarily being of itself pertinent. Also, the following comments contain conclusions and observations which have only been drawn or become apparent after conception of the subject invention.
Hydraulic drives generally are propelled by oil or another hydraulic fluid which is delivered to the drive by a delivery hose or line, to be removed from the drive by a return hose or line. Frequently, the hydraulic fluid is stored in a reservoir and is pressurized by a pump which propels the fluid from the reservoir to the drive.
While hydraulic drives have many advantages, they do lack an on-off switching device that would be as convenient, compact and inexpensive as an electric motor on-off switch. Since many hydraulic drives and tools are operated at a distance from the hydraulic power source, there exists a need for a conveniently and safely actuable control facility right at the tool or drive itself.
In response to such need, the delivery and return hoses have sometimes been cut in the vicinity of the tool and have there been provided with a manually actuable valve having an open position for providing an interconnection between the delivery and return hoses, and an alternative closed position blocking that interconnection. In the open position of that valve, the hydraulic drive was effectively bypassed, thereby deactivating the drive. In the valve's closed position, fluid was free to flow to and from the drive through the delivery and return hoses, respectively.
One drawback of such a makeshift approach was its requirement of several fittings at the actuable bypass valve location. Another drawback was the floating character of the valve between frequently dangling hoses. This has raised the question whether such an on-off valving facility would always be safely operable.
Another, perhaps even more serious drawback of such an approach stems from its makeshift character. Thus, the high pressure building up at the inserted bypass valve in its closed position frequently caused lines to break, discharging the hydraulic fluid over the environment and endangering the working crew. Also, there was no assurance that personnel cutting into hoses or otherwise providing a bypass valve therebetween would in fact use a valve appropriate to the particular tool or drive.
For instance, if a valve suitable for a small tool would be used for a large drive, there was the danger that the valve in its open position would not completely bypass the drive, so that the same could start operating despite a supposedly "off" condition, thereby exposing the operator to damage or injury. In this respect, a matter of primary concern to the manufacturer was simply beyond the manufacturer's control.
In some hydraulic tools, these drawbacks have been alleviated by the manufacturer's providing manually actuable valving at the particular tool itself. In practice, such valving has been provided at or near a tool handle. Typically, such valving is of a type which has to be constantly engaged to remain in an active position, and which will automatically revert to its rest position upon release of the manual engagement. This is, however, not always convenient in practice, particularly not in instances where a continuous presence of the worker's or operator's hand at the machine would be burdensome or dangerous.
Also, the special provision of valving at particular tool handles does not generally represent a feasible, convenient or effective approach for retrofitting hydraulic drives with a valving facility.
A growing need for retrofitting facilities of hydraulic drives has, consequently, remained unsatisfied prior to the subject invention.